1. Field of the Invention
The present invention relates to a camera system, lens unit and accessory device. More particularly, the present invention relates to a camera system in which a lens unit and other elements can be combined with ensured propriety, and such a lens unit and accessory device.
2. Description Related to the Prior Art
A camera system known in the art is a combination of a lens unit and a camera main body. The lens unit accommodates a photographing lens. The main body supports the lens unit removably. It is possible to load one of the main body and the lens unit with an accessory device, for example an electronic flash unit, a conversion lens device, and the like. It is known to mount the accessory device between the main body and the lens unit, for example a rear converter for changing a focal length or subject distance.
There occurs a change in the aperture stop or focal length between photographing with the accessory device and photographing without the accessory device, such as a conversion lens device and rear converter. If a type of the accessory device is not suitable for the lens unit or the camera main body, there occurs a problem in impropriety in the automatic exposure control or automatic focus adjustment.
JP-A 6-027515 and JP-A 2002-072328 disclose a camera system in which the lens unit has CPU, and the CPU, upon setting the accessory device between the lens unit and the camera main body, detects existence and type of the accessory device to supply the main body with type data of the accessory device by transmission. U.S. Pat. No. 6,707,992 (corresponding to JP-A 2002-258380) discloses a camera system in which a rear converter as the accessory device is settable between the lens unit and the main body. An intermediate communicating terminal is disposed in the rear converter for transmission between the lens unit and the main body. Type data of the rear converter is transmitted to the main body in transmitting type data of the lens unit to the main body. U.S. Pat. No. 6,738,574 (corresponding to JP-A 2003-228114) suggests a camera system in which a determiner is incorporated in the main body, and compares the accessory type data with the camera main body type data upon setting the accessory device on the main body, to check propriety between the main body and the accessory device.
In the constructions disclosed in those documents, type data of the accessory device and the lens unit are transmitted to the camera main body. The determiner in the main body checks propriety of the accessory device or the lens unit. If the main body does not have the determiner, propriety cannot be checked. No known camera system is successful in determining propriety of the accessory device of the lens unit.